WO2019174719A1

WO2019174719A1 - Polycrystalline ceramic solid body and method for producing a polycrystalline ceramic solid body

Info

Publication number: WO2019174719A1
Application number: PCT/EP2018/056263
Authority: WO
Inventors: Manfred Schweinzger
Original assignee: Tdk Electronics Ag
Priority date: 2018-03-13
Filing date: 2018-03-13
Publication date: 2019-09-19
Also published as: US11680021B2; CN112566882A; JP7113904B2; EP3765427A1; EP3765427B1; EP4234515A3; US20210078907A1; EP4234515A2; JP2021516204A

Abstract

The invention relates to a polycrystalline, ceramic solid body comprising a main phase having a composition of the following general formula: (1-y)Pb_a (Mg_bNb_c) O_3-e + yPb_aTi_dO₃, wherein 0.055 ≤ y ≤ 0.065; 0.95 ≤ a ≤ 1.02; 0.29 ≤ b ≤ 0.36; 0.63 ≤ c ≤ 0.69; 0.9 ≤ d ≤ 1.1; 0 ≤ e ≤ 0.1, and optionally one or more additional phases, wherein, in each section through the solid body, the surface portion of the additional phases is less than or equal to 0.5% in relation to a random cross-section through the solid body, or wherein the solid body is free of additional phases. The invention also relates to an electrode having the ceramic solid body and a device having the electrode, as well as a method for producing the solid body and the electrode.

Description

description

Polycrystalline ceramic solid and process for producing a polycrystalline ceramic solid

The invention relates to a polycrystalline, ceramic solid. Furthermore, the invention relates to an electrode comprising the ceramic solid. Finally, the invention relates to a method for producing a ceramic solid and an electrode comprising the solid.

A variety of ceramic electrode materials are known in the art. There is a great demand for materials that are suitable for use in electrodes and show improved properties with regard to efficiency and power loss of the electrodes.

It is therefore an object of the present invention to provide new materials which are suitable for use in electrodes.

This object is achieved by a material according to claim 1. Accordingly, according to a first aspect, the invention relates to a polycrystalline, ceramic solid body

a main phase having a composition of the following general formula:

(1-y) Pb _{a (} Mg _bN b _c) 0 _3-e + yPb _a Ti _d 0 ₃

with 0.055 <y <0.065;

0.95 <a <1.02;

0.29 <b <0.36;

0, 63 <c <0.69;

0.9 <d <1.1;

0 <e <0, 1; - And optionally one or more secondary phases, wherein in each section through the solid surface area of the minor phases relative to any section through the solid surface is less than or equal to 0.5 percent, or wherein the solid body is free of secondary phases.

A polycrystalline solid here is to be understood as meaning a crystalline solid which has crystallites, which are also referred to below as grains. The crystallites are separated by grain boundaries. The solid contains grains that are the material of the

Main phase or consist of it. The solid is sintered in particular.

The solid has a major phase with the general formula

(1-y) Pb _{a (} Mg _bN b _c) 0 _3-e + yPb _a Ti _d 0 ₃ on. This is a single-phase system. The lead magnesium niobate component, Pb _a (MgbNbc) C> 3-e, and the lead titanate component, Pb _a Ti _d C> 3, thus together form a solid solution, ie a single phase, which is the

Main phase of the polycrystalline ceramic solid is. The main phase is characterized by a perovskite structure.

The polycrystalline, ceramic solid may have one or more other phases other than the main phase, which are referred to below as secondary phases. It is a central feature of the invention that the solid has only a small proportion of secondary phases or is completely free of secondary phases. Thus, in any section through the solid, the area ratio of all secondary phases is calculated based on the Cut surface through the solid, less than or equal to 0.5 percent.

It is preferred if the solid is free of secondary phases. In this case, the solid contains only the main phase and has no secondary phase. In particular, the

Solid body consist of the main phase.

Under a secondary phase is basically every one in her

To understand the composition of a phase other than the main phase. Without being bound by theory, the minor phase may be an Mg-rich composition other than the major phase composition, such as a Mg2 _/ 3Nbi _/ 303 phase. An Mg-rich

Secondary phase has in contrast to the main phase increased Mg content. For example, the Mg-rich secondary phase can also be Pb-poor at the same time, ie have a lower content of Pb than the main phase.

For example, a minor phase can also be a Pb-rich secondary phase, ie a minor phase which has a higher Pb content than the main phase.

Since secondary phases differ in their elemental composition from the main phase, it is possible that

Area fraction of the secondary surface based on a sectional area through the solid to quantify using elemental distribution images. Such elemental distribution images can be obtained by SEM-EDX measurements (SEM stands for Scanning Electron Microscopy, EDX stands for Energy Dispersive X-Ray Spectroscopy). The polycrystalline ceramic solid according to the invention is characterized by a high mechanical stability. Components such as electrodes formed from this material are therefore robust and durable.

In addition, solids of the invention have a high

Breakdown voltage on. Such is important for safe use as electrode material.

The solid according to the invention is suitable not least because of its high dielectric constant and capacity for use as electrode material.

The described composition of the main phase allows an unexpectedly high capacity in a temperature range between 20 and 45 ° C, in particular between 30 and 42 ° C. A high capacity in this area is particularly favorable for use in a number of ceramic electrodes. The

Maximum capacity can be, for example, by the proportion of lead titanate, y, within the formula

(1-y) Pb _{a (} Mg _bN b _c) 0 _3-e + yPb _a Ti _d 0 _{3 set} variably. By choosing y in the range of 0.055 <y <0.065, it is possible to achieve ceramic solids which reach a maximum of the electrical capacity in the region of the body temperature of mammals.

The inventors have recognized that with the aid of the y-content, the capacity can be adapted to the particular temperature at which the electrodes are operated. It is thus possible to set a maximum capacity for the respective desired operating temperature. Solids with 0.055 <y <0.065 are for electrodes

suitable, which are operated in a temperature range between 20 and 45 ° C. A y-content between 0.055 and 0.065 is especially in the temperature range between 30 and 42 ° C, e.g. at a temperature of 35 and 40 ° C (e.g., 37 ° C) is particularly advantageous. Electrodes based on a solid of this composition not only have a very high capacity in said temperature range but also a very low loss factor and a low

Self-heating.

The polycrystalline ceramic solid according to the invention additionally differs from conventional ceramic solids in that it has no or only a very small proportion of secondary phases. The inventors of the present invention have observed that in US Pat

conventional manner produced, ceramic solids containing a main phase of a comparable chemical composition a significant proportion of secondary phases

is available.

Further, it has been found by experiments of the inventors of the present invention that these minor phases reduce the electric capacity of the solid. However, a high capacity is desirable for use in electrodes.

In addition, the inventors of the present invention were able to experimentally observe that in conventional

ceramic phases present secondary phases when used in high-capacitance ceramic electrodes to a lower power dissipation. This leads to higher energy losses and thus to lower efficiency. The higher electrical losses and their release in the form of heat also lead to a self-heating of the solid. Such self-heating is undesirable. It is the result of energy losses in the form of waste heat and indicates low efficiency. In addition, self-heating is also undesirable, since the heat in the vicinity of the electrode can cause damage or can be perceived as unpleasant to the touch.

By setting a proportion of minor phases of less than or equal to 0.5 percent (area fraction based on arbitrary cut surface through the solid), the inventors of the present invention have succeeded

Dielectric constant and increase the electrical capacity. Improved power dissipation has also been achieved, which improves the efficiency of use in ceramic electrodes and reduces unwanted self-heating.

These positive effects are the more pronounced the lower the proportion of secondary phases on the solid.

In addition, the inventors of the present

Invention observe that by avoiding a significant proportion of secondary phases and the optical

Change the appearance of the ceramic solid. This is how traditional ceramic solids are characterized

Often a yellowish hue. In contrast, the inventive

ceramic solids no comparable yellow color.

The lower the proportion of secondary phases on the solid, the lower the yellowish color content. The yellowish color thus reflects the presence of minor phases. By contrast, the ceramic solid according to the invention is distinguished by a slightly beige hue.

According to an embodiment of the invention,

polycrystalline, ceramic solid is at each

Section through the solid the area fraction of the

Secondary phases, based on any sectional area through the solid, is less than or equal to 0.3 percent, preferably less than or equal to 0.1 percent, more preferably less than or equal to 0.05 percent, particularly preferably less than or equal to 0.01 percent. Most preferred is when the polycrystalline ceramic solid is free of minor phases.

The smaller the proportion of secondary phases on the solid, the higher is the dielectric constant, the electrical

Capacity and the lower are the power losses.

Consequently, a lower proportion of secondary phases also leads to a lower self-heating. It also participates

decreasing proportion of secondary phases from the yellowish tint of the ceramic solid.

In one embodiment, the solid is free of

Pyrochloren, such as the stable cubic

Pyrochlore phase Pb3Nb40i3. Pyrochlore phases occur especially when free Nb2Ü5 is present during sintering or when there is a lack of PbO.

According to one embodiment, the inventive

Solid no Mg and / or Nb-rich secondary phase, in particular no Mg-rich secondary phase. For example, the solid contains without regard to the exact Formula to be bound by theory, no Mg2 _/ 3Nbi _/ 3C> 3 phase. Such Nebenphasen can especially with a

Lack of Pb arise during sintering, which can occur, inter alia, during sintering by exhaust gases from PbO.

According to a further embodiment, the solid according to the invention does not have any Pb-rich secondary phase. The

Inventors have recognized that not only a deficit but also an excess of Pb can lead to the formation of undesirable secondary phases. Pb-rich secondary phases, like the other secondary phases described above, lead to a reduction in the electrical capacity.

One embodiment relates to the solid according to the invention, where: 0.057 <y <0.063, for example, y is 0.06.

A further embodiment relates to the solid according to the invention, wherein the following applies for the coefficient a:

0, 96 d a d 1.02, preferably 0.97 <a d 1.01, more preferably 0.97 <a d 1.00, and most preferably a = 1.0.

One embodiment relates to the solid according to the invention, wherein for the coefficient b: 0.31 <b <0.36. Preferably, b: 0.33 d b d 0.35.

One embodiment relates to the solid according to the invention, wherein for the coefficient c: 0.63 <c <0.68. Preferably, for c: 0.64 <c <0.66. If c is less than 0.68, in particular less than 0.66, the inventive ceramic solid has no increased up to a slightly reduced Nb content, which is beneficial to the

Prevention of Pyrochlorphasen effects. Another embodiment relates to the solid according to the invention, wherein for the coefficient d: 0.95 ddd 1.05, preferably d = 1.0.

One embodiment relates to the invention

ceramic solid, where e holds: 0 <e <0.09.

Preferably, e is 0. In this case, applies to the

Composition of the main phase the general formula:

(1-y) Pb _a (Mg _b Nb _c ) 0 ₃ + yPb _a Ti _d 0 ₃

Depending on the valences, for example of niobium, in the first component may occur the case

Oxygen content of the component (1-y) Pb _a (MgbNbc) 0 ₃ from the value of 3 to values deviates slightly smaller than the third This deviation is preferably less than 0.09. As a rule, there is no significant deviation and e is equal to 0.

A further embodiment relates to the solid according to the invention, wherein the main phase has grains or consists of grains whose average grain size d5 _Q , measured as numerical median value by static image analysis, greater than 4.0 pm, preferably greater than 4.5 pm, particularly preferably greater than 5.0 pm.

For example, the average particle size d5 _Q , measured as a number-related median value by static image analysis, lies in a range between 4.0 and 9 μm, preferably between 4.5 and 8 μm, more preferably between 5.0 and 7 μm,

more preferably between 5.0 and 6.0 pm.

Preferably, the individual grains in the static image analysis, over a mean diameter on the

Basis of the so - called circle equivalent diameter (English: "equal circle diameter (ECD)")

Grains or crystallites of a polycrystalline solid have an irregular three-dimensional structure.

By means of an EDX / EBSD analysis in the scanning electron microscope, a 2D projection of the grains can be obtained (EDX / EBSD overlay image). In this way, the grain size can be calculated over the size of the area of the 2D projection of the grain

express. Finally, the ECD can be determined from the latter area. For this purpose, the diameter of a circle is calculated whose area corresponds to the measured 2D projection of the grain. In this application, mean grain sizes are thus determined over the area average.

Larger mean grain diameters require larger "domains" in the solid, ie areas within which electrical dipoles have the same orientation, which in turn the formation of larger dipole moments and thus a higher

Dielectric constant e for the solid body brings with it. This is a corporative effect which in total causes an increase in the electrical capacitance of the polycrystalline, ceramic solid. The larger the mean grain size, the higher the consequently

electrical capacity.

The inventors of the present invention have found that by a procedure that avoids secondary phases, at the same time polycrystalline, ceramic solids with larger average grain sizes d5 _Q , measured as number-related

Median value obtained by static image analysis. The avoidance of secondary phases and the production of larger grains are therefore related to one another and make it possible to improve the electrical properties of the ceramic solid. According to one embodiment, the solid has pores. However, solids according to the invention preferably show a low porosity overall and consequently tend to be none

significant absorption of moisture, which the

electrical properties undesirably

could influence. For example, the pore volume based on the total volume of the solid may be less than 10%, preferably less than 5%, particularly preferably less than 2%. It is also conceivable that the solid body is free of pores. The low tendency to absorb

Moisture is reflected in the fact that in an impedance measurement in saline solution the open circuit voltage (OCV = open

Circuit potential) is obtained.

According to one embodiment, the solid has a

Press density of 4 to 5.5 g / ml, preferably 4.5 to

5.9 g / ml, e.g. 4.8 g / ml.

According to one embodiment, the ceramic solid according to the invention has a DC resistance greater than 10 ⁸ ohms in the context of impedance measurements.

According to one embodiment, the inventive

Solid state in liquid environment, a breakdown voltage greater than 4000 V on. This allows a secure

Application .

According to one embodiment, the ceramic solid has a capacity of over 50 nF at 200 kHz and 1 V in a temperature range of 30-42 ° C, in particular over 52 nF, for example 52-58 nF. In one embodiment, the maximum capacitance of the ceramic solid is at least 53 nF, eg 53-58 nF at 200 kHz and 1 V in one

Temperature range of 30-42 ° C.

According to one embodiment, the inventive

Solid does not show any cracks visible to the human eye. The composition according to the invention has good homogeneity and stability, so that cracking can be avoided.

A second aspect of the present invention relates to an electrode comprising a polycrystalline ceramic solid according to the first aspect of the invention and

Furthermore, an applied on the solid electrical contact.

One provided with an electrical contact

Ceramic solid according to the invention forms a

Electrode.

According to one embodiment, the inventive

Electrode exactly a ceramic according to the invention

Solid and exactly one electrical contact on.

According to one embodiment, the electrical

Contacting a noble metal, especially silver on or consists of silver. Silver tends, even if it is high

Temperatures is exposed, not to corrosion. It is also solderable and easy to work with.

According to one embodiment, the electrical contact is fixedly connected to one side of the ceramic solid body and only with a tensile value greater than 35 N from the ceramic To separate solids. Thus, an electrode is obtained with a contact, which is particularly resistant to tensile.

A third aspect of the invention relates to a method of producing a polycrystalline ceramic solid

a main phase with a composition of

following general formula:

(1-y) Pb _{a (} Mg _bN b _c) 0 _3-e + yPb _a Ti _d 0 ₃

with 0.055 <y <0.065;

0.95 <a <1.02;

0.29 <b <0.36;

0, 63 <c <0.69;

0.9 <d <1.1;

0 <e <0, 1;

- and optionally one or more secondary phases,

with every cut through the solid state of the

Area fraction of the minor phases is less than or equal to 0.5 percent, based on any sectional area through the solid, or the solid is free of secondary phases,

comprising the method steps:

A) providing starting materials comprising the

Elements Mg, Nb, Ti and Pb;

B) producing a mixture comprising the starting materials

C) calcining the mixture to produce a

calcined mixture

E) processing the calcined mixture into a

green body

F) sintering of the green body,

being to control the lead budget

Step F) takes place in a closed system, and / or in step A) or another step F)

previous steps a Pb having

Starting material is added in excess.

The polycrystalline ceramic solid produced by the process is in particular a solid according to the first aspect of the invention. All described as beneficial in this context

Embodiments of the ceramic solid are also to be considered in terms of the method as a further embodiment forms.

Under a closed system according to the present invention, in particular a system - e.g. a container that can be designed as a capsule - understand that allows no gas exchange with the environment.

The inventive method allows the control of the lead budget, the emergence of undesirable

To avoid secondary phases.

By contrast, conventional sintering processes lead to an uncontrolled loss of lead. In particular, Pb can outgas in a furnace in the form of PbO during sintering. At the high sintering temperatures, the green body thus becomes Pb

deprived, which locally leads to the formation of Pb-poor or Mg-rich secondary phases. This is prevented in the process according to the invention by adding lead in excess prior to the sintering process or by sintering in a closed system which efficiently outgasses PbO

in derogation. In particular, both measures can

be combined with each other, as even in a closed system, although a limited amount of PbO in the Gas phase can pass, even if a saturation occurs and they can not leave the closed system. By combining a Pb excess and

Simultaneous sintering in a closed system could be particularly effectively reduced or completely avoided secondary phases. An initial Pb excess also helps prevent pyrochlore phases as minor phases.

The inventors of the present invention were able to determine that the method according to the invention unexpectedly not only makes it possible to avoid secondary phases, but at the same time leads to larger particle sizes of the polycrystalline, ceramic solid. This, together with the avoidance of unwanted secondary phases, makes it possible to increase the dielectric constant of the resulting ceramic

Solid. In addition, improved capacity and lower power losses will be obtained and unwanted yellowish tinting avoided.

The starting materials which are provided in step A) may be, for example, oxides, hydroxides, carbonates, nitrates, acetates or comparable salts of the elements Mg, Nb, Ti and Pb. They are preferably oxides of the elements Mg, Nb, Ti and Pb and also oxides of two or more of the elements Mg, Nb, Ti and Pb. These

Compounds are usually available at reasonable prices commercially or can be prepared without much experimental effort.

According to one embodiment of the method according to the invention, a first starting material is provided in step A), which is a starting material containing Mg and Nb. It is preferable if the first Starting material around Mgi _{/ 3} Nb _2/3 C> ₂ acts. The usage of

Mgi _/ 3Nb _2/3 C> ₂ as the first starting material favors the avoidance of undesired pyrochlore phases, such as Pb ₃ Nb ₄ 0i ₃ , as

Secondary phases. If Mgi _{/ 3} Nb _2/3 C> _{2 is} chosen as the first starting material, the method can also be referred to a method according to the Columbit method.

According to one embodiment of the method according to the invention, step A) is preceded by a separate step A0) for the production of Mgi _/ 3Nb _2/3 C> ₂ . Mgi _{/ 3} Nb _2/3 C> ₂ can be, for example, magnesium oxide (MgO) and niobium oxide (Nb ₂ 0s), for example by wet grinding, followed by drying (filter press,

Spray drying), then calcining and

if necessary, produce a final grinding step.

According to one embodiment of the method according to the invention, a second starting material is provided in step A), which is a Ti-containing starting material. Preferably TiC> ₂ serves as a second starting material. TiC> ₂ is comparatively inexpensive and readily available.

According to a further embodiment of the method according to the invention, a third starting material is provided in step A) which is a Pb-containing one

Starting material is. In particular, the Pb oxides, PbO and Pb ₃ 0 ₄ , have proven to be well suited. They allow a good reaction and support the control of the lead budget.

In one embodiment, the third starting material is Pb _3Ü4 . Pb _3Ü4 decomposes at temperatures above 500 ° C and releases PbO. Pb ₃ 0 ₄ has a lower toxicity than PbO, so its use is the Work safety improved. By choosing Pb ₃ C> ₄ instead of PbO it is possible to assemble the

Making reaction vessels and reactors safer. This is especially true for large-scale and industrial

Production of the ceramic solid matter.

According to one embodiment, the starting materials in step A) in stoichiometric proportions to each other

provided. In this case, step F) is performed in a closed system to prevent loss of Pb in sintering by outgassing PbO.

According to a further embodiment, in step A) all non-Pb-containing starting materials are provided in stoichiometric proportions to each other, while the Pb-containing starting material is added in excess. The inventors of the present invention have found that a Pb excess in step A) prevents Pb-poor or

Mg- and / or Nb-rich secondary phases allows.

According to a preferred embodiment, the excess of the Pb-containing starting material (or the third

Starting material) in such a way that the Pb content of all supplied starting materials is up to

0.02 mol per 1 mol Pb of the composition of the main component to be obtained, (1-y) Pb _{a (} MgbNb _c) Cb-e + yPb _a Ti _d 0 ₃ .

Preferably, said excess is between 0.01 mol and 0.02 mol. The inventors of the present invention have observed that both Pb-poor and Pb-rich secondary phases can be avoided particularly well in the latter case. According to a further development, the starting material containing Pb is PbO. In this case, the

Provided starting materials in an amount such that their stoichiometry to each other theoretically a composition after a reaction without Pb losses of the following

general formula would result:

(1-y) Pb _{a (} Mg _bN b _c) 0 _3-e + yPb _a Ti _d 0 _{3 +} x PbO,

where a to e are defined as given above and where 0 d x <0.02. Preferably, 0 <xd 0.02, more preferably 0.01 <c <0.02. PbO will be in one

Excess up to 0.02 mol added, so that the

Composition has up to 0.02 mol excess Pb per 1 mol of aspired Pb in the main phase.

_Analogously , instead of PbO, Pb _3Ü4 can be _present in excess

be added. If it is the Pb-containing

Starting material is Pb _3Ü4 , Pb is _3Ü4 in an excess up to 0.0067 mol per 1 mol of Pb to be achieved

Composition of the main component added. Since 1 mol

Pb ₃ 0 ₄ releases 3 mol of PbO, this in turn corresponds to a Pb excess of up to 0.02 mol. Preference is given to Pb _3Ü4 in an excess between 0.0033 mol and 0.0067 mol

added. This proportion of the starting material Pb is _3Ü4

especially suitable for avoiding secondary phases and good ones

To achieve grain sizes.

According to one embodiment, the generation of a

Mixture in process step B) by grinding the

Starting materials, in particular wet milling. In wet-milling, the comminution of the starting materials is carried out in a suspension, e.g. an aqueous suspension.

The milling is continued until the starting materials powder or suspensions with particle sizes of d50, measured as numerical median value by static image analysis, <1.5 pm, preferably <1 pm.

Mixtures with grain sizes of the type mentioned lead to good results in further processing. They allow a good mixing and make it easier to achieve a good homogeneity during the calcination.

According to one embodiment of the method according to the invention, wet grinding is followed by a drying step B1). The drying step is used to prepare the

Calcination.

According to one embodiment, the calcination step C) takes place at a temperature between 800 and 860 ° C, for example at 840 ° C. These temperatures ensure effective removal of moisture.

According to a development of the just mentioned embodiment, the calcining step C) is not carried out in a closed system, such as a closed container, according to step F). This is not necessary as the

indicated temperatures are not high enough to cause a significant PbO loss. However, it is also possible in principle to carry out the calcining step in a closed system.

According to one embodiment, the method according to the invention comprises a step D), in which TiCt and / or Nb2Ü5 is added to the calcined mixture. Step D) preferably takes place after step C) and before step F). The addition of TiC> 2 and / or Nb2Ü5 makes it possible to shift the maximum of the electrical capacitance of the ceramic solid as a function of the temperature or

to adjust.

In addition, the addition of TiCb and / or Nb2Ü5 in step D) allows excess lead, such as PbO, within the calcined mixture to form

To consume perovskite phases. The addition of T1O2 and / or Nb2Ü5 in process step D) thus represents another

For example, the combination of an initial excess of Pb, which is beneficial in avoiding pyrochlore phases, allows in

Combination with the addition of T1O2 and / or Nb2Ü5 in step D) to reduce the initial Pb excess and thus increase the risk of excess Pb in the final solid

prevention. The latter leads to a decrease in the

Dielectric constant or capacity.

In one embodiment, the proportion of added T1O2 and / or Nb2Ü5 based on the calcined mixture is up to 0.4 weight percent, preferably 0.001 to 0.4

Weight percent, more preferably 0.01 to 0.4

Weight percent, particularly preferably 0.1 to 0.4

Percent by weight based on the weight of the calcined mixture.

One embodiment relates to the process according to the invention, wherein in step A) a starting material containing Pb is added in excess and the process according to the invention also comprises a step D) after step C), in which T1O2 and / or Nb2O5 is added to the calcined mixture. In addition, it is preferable if at the same time step F) takes place in a closed system. Instead of evaporating excess lead, it is for example possible to add TiCh and / or Nb _2Ü5 in a step D), which binds the excess lead. This has the opposite of the evaporation of excess PbO in the sintering step

Advantage that the resulting polycrystalline ceramic solid as a whole is much more homogeneous. The diffusion rate of lead in the solid state is several

Orders of magnitude less than in the gas phase. This results in excess, near-surface PbO leaving the solid more rapidly during sintering than PbO from the interior of the solid

Solid can nachdiffundieren. In particular, when sintering is not done in a closed system, particularly large amounts of PbO are vaporized. This leads to local inhomogeneities in the solid state due to the differences in the diffusion rates, which in turn causes the

Formation of undesirable secondary phases favors. It is thus particularly advantageous if excess Pb, the

For example, in step A) in the form of an excess of the Pb-containing starting material (third starting material) was added, by adding T1O ₂ and / or Nb _2Ü5 in step D) is compensated, at the same time sintering in one

closed system takes place.

One embodiment relates to the process according to the invention, wherein step E) comprises:

Grinding the calcined mixture,

Putting the calcined mixture with a

Binder,

Spray-drying the calcined mixture with binder to produce a ceramic granulate

- Pressing the ceramic granules to produce the

Green body. The grinding of the calcined mixture is here preferably continued until the resulting particle size of d50, measured as a numerical median value by static

Image analysis <2 pm, preferably <1 pm e.g. is about 0.8 pm. Optionally, milling is carried out in step E) together with the calcined mixture T1O2 and / or Nb2O5 added in an optional step D). A fine one

Grinding favors the preservation of a homogeneous green body.

The proportion of binder based on the weight of

Calcined mixture is preferably between 0.5 and 10 weight percent, more preferably between 1 and 5

Weight percent, especially between 2 and 4

Percent by weight, for example 3% by weight. The binder may, for example, be a PVA binder (PVA = polyvinyl alcohol).

By spray-drying the calcined mixture with binder, a ceramic granules is obtained, which is characterized by

Pressing can produce a green body.

The green body passes through the sintering according to step F) in the ceramic solid according to the invention according to the first aspect of the invention.

According to one embodiment of the method according to the invention, step F) is carried out at a maximum temperature of 1150 to 1280 ° C. For example, the process can be carried out at a maximum temperature of 1250 ° C.

According to one embodiment, the maximum temperature during step F) is held for 1 to 6 hours, for example 4 hours. These temperatures and holding times during sintering allow, in addition to a complete reaction of the starting materials, good homogeneities of the resulting ceramic solid, which assists in avoiding unwanted secondary phases.

According to one embodiment of the method according to the invention, step F) takes place in a closed system, wherein the closed system is a closed container.

Under a closed container in the context of the present invention, in particular, a container is to be understood, between the interior and the environment no gas exchange takes place.

According to one embodiment, the container has a height of 10-40 cm, e.g. 15-25 cm, a width of 20-50 cm, e.g. 25-35 cm and a depth of 30-50 cm, e.g. 35-45 cm up.

According to one embodiment, the closed container comprises at least one of the materials selected from the group of Al 2 O 3, ZrCb and MgO, or the container is made of one of these materials.

Preferably, the closed container comprises or consists of MgO. The inventors have found that MgO is particularly well suited because it is unusually high

Tightness against PbO has and also not to

Absorption of PbO tends. For example, MgO allows better sealing against PbO than is possible with conventional container materials such as cordierite or mullite. In particular, MgO tends in contrast to other metal oxides also not for the absorption of PbO.

In this way, better shielding can be achieved than with conventional container materials, so that outgassing of PbO can be better prevented than with other materials, e.g. with cordierite or mullite as container material.

According to one embodiment, the closed container has a container body and a container plate which

preferably containing or consisting of the just mentioned materials.

According to one embodiment, a plurality of green bodies

simultaneously sintered in the closed container.

For example, several stacks of green bodies

be sintered simultaneously in the closed container. For example, 5 to 25 stacks of 5 to 30 each

Green bodies are sintered in the container. In this way, the presence of multiple green bodies rapidly saturates PbO in the closed container

achieved, whereby a high undesirable lead loss can be avoided.

A preferred embodiment relates to the inventive method, wherein the closed container has an interior in which one or more green bodies are arranged, so that the Volumenfüllgrad all green bodies based on the volume of the interior at least 30 vol.%, Preferably at least 40 vol.%.

The volumetric fill factor gives the ratio of the total volume of all green bodies in the interior of the closed Container arranged and sintered, based on the total volume of the interior of the closed container.

Volume of all green bodies

Volumetric efficiency = -; -; -; - 100 [Vol. %]

Volume interior container

If there is only one green body in the closed container, the "volume of all green bodies" is equal to the volume of this single green body

"Volume of all green bodies" equal to the sum of the individual volumes of the green bodies, which are arranged in the interior of the closed container.

A volume fill level of 0% by volume would mean that the closed container is empty, ie contains no green body. A volume fill level of 100% by volume would mean that the container is completely filled with the green body (s), with no gaps remaining.

The inventors of the present invention have observed that a volume fill level of at least 30% by volume is particularly well suited to minimize Pb losses on sintering. At a volume filling level of at least 30% by volume, saturation of PbO in the interior of the closed container can be achieved rapidly. In this way, the transfer of further PbO into the gas phase is made more difficult. This makes it possible to reduce a preferably present excess Pb in the green body during sintering slowly and in a controlled manner. A deficit in Pb in the resulting ceramic

Solid state can be reduced or completely avoided, which helps to avoid unwanted secondary phases.

The lower the volume filling level of the container, the more PbO goes into the gas phase in the interior of the closed Container over and more the control of the

Lead budget difficult.

Even better, a volume filling level of at least 40% by volume is suitable. This allows a particularly efficient control of the lead budget.

According to another embodiment, the volume filling level is less than 60 vol.%. The inventors have recognized that it is favorable if the volume filling degree does not exceed 60% by volume. If the Volumenfüllgrad is higher, the green body can be difficult so closed

Arrange containers that they are sufficiently separated from each other to be sintered together.

According to a particularly preferred embodiment, the Volumenfüllgrad is between 30 and 60 vol.%, Preferably between 40 and 60 vol.%. In this case, neither a significant Pb excess nor a larger Pb deficit occurs in the

resulting ceramic solid according to the invention, with the result that Pb-rich as Pb-poor secondary phases can be avoided.

For example, the inventors have observed that a volumetric filling level of 45% by volume of the green bodies in a container containing MgO merely results in a weight loss of the

Green body of about 0.6 weight percent due to evaporation of PbO leads. Such a low lead loss allows an excellent lead balance control and thus an effective avoidance of unwanted secondary phases.

According to one embodiment, the Volumenfüllgrad is at least 30 vol.% And at the same time is the first starting material Mgi _/ 3Nb2 _/ 3C> 2 and the Pb-containing starting material is Pb3Ü4, wherein the ratio of the molar amounts of Mgi _/ 3Nb2 _/ 3C> 2 and Pb3Ü4 is 1: 0.34 to 1: 0.38, preferably 1: 0.35 to 1: 0.37, more preferably 1: 0.355 to 1: 0.36, for example 1: 0.356 to 1: 0.358. These framework conditions allow for excellent lead balance control while maintaining high safety requirements while maintaining a high level of safety

ceramic solid, which is free of secondary phases and allows excellent values in terms of capacity and power loss. Furthermore, in this case, the Ti-containing starting material may be, for example, T1O2 and the

Ratio of the amounts of Mgi _/ 3Nb2 _/ 3C> 2 and the Ti-containing starting material may for example be 1: 0.055 to 1: 0.065.

According to one embodiment, the sintering takes place in an oven in which the closed container is arranged. Another important effect of the method according to the invention is that the use of a closed container in step F) protects the furnace used for sintering from PbO exhaust gases. Pb-containing exhaust gases cause the

Inner lining of the furnace over time absorbs a significant amount of Pb. This leads to damage to the materials used for the interior trim. Since these often contain silicates or aluminosilicates, they tend to "glaze" when lead is taken up, but also other types of

Interior paneling of ovens can be damaged by Pb intake. The interior lining becomes brittle over time due to the uptake of lead, gets cracks and has to be renewed. The inventors of the present invention have realized that this can be particularly effectively prevented by sintering in a closed container preferably comprising or consisting of the aforementioned materials. A fifth aspect of the present invention relates to a method for producing an electrode according to the second aspect of the present invention, comprising a method of producing a polycrystalline ceramic

Solid according to the fourth aspect of the present invention

Invention and comprising an adjoining

Step to provide the solid with an electrical contact.

According to one embodiment, the electrical

Contacting by applying and baking a paste, wherein the baking is preferably carried out at a temperature of 680 to 760 ° C. Preferably, the paste is a silver paste. Silver is corrosion resistant, solderable and allows a strong bond with the polycrystalline, ceramic even at high temperatures

Solid state.

General Synthesis Example

The following are the methods according to the fourth and fifth aspects of the invention by way of example

Synthesis route will be further explained.

The stoichiometry of the starting materials to be supplied is chosen so that their quantity corresponds to the following formula:

0, 94 * Pb (Mgi _/ 3Nb _2/3) 0 ₃ + 0, 06 * PbTiO ₃ + x * PbO

with 0 <x <0.02.

The weighed PbO excess of up to 0.02 mol per 1 mol Pb of the composition of the main phase decreases

finally in the course of the sintering process. The preparation is carried out starting from a Mg- and Nb-containing starting material, such as Mgi _/ 3Nb2 _/ 3C> 3, for example by the so-called columbite method. The starting material containing Mg and Nb is dried with a starting material containing Pb, eg Pb.sub.3 U.sub.4, and a Ti-containing starting material, eg TiCh, wet milling (particle size d.sub.50 <1 .mu.m), and at a temperature between 800-860 Calcined ° C. The Pb-containing starting material is for this purpose preferably provided in excess. The finished sales powder is optionally combined with (additional) T1O2 or Nb ₂ O (0 to 0.4

Weight percent based on the weight of the sales powder) and finely ground with a binder, e.g. PVA binder added. Subsequently, the resulting mixture is spray-dried, so that a press-capable ceramic granules is formed. The

Granules are pressed into green bodies and sintered. The sintering is carried out at 1150-1280 ° C with the sintering temperature held for 1-6 hours. To control the

Lead household will be sintered in a closed house

Container in the form of a capsule of MgO at a

Volume fill level of> 30 vol.% Performed.

The container may in particular have a container body and a container plate. Container body and container plate in combination with each other form the container. They are arranged on top of each other so that the container

closed is.

This procedure is easy for the purpose of a

Extend mass production by using correspondingly large containers or a large number of containers in the sintering furnace. The process provides polycrystalline, ceramic solids that are free of minor phases. In the course of compression, the geometry of the poly-crystalline, ceramic solid can be designed. The electrical contact is obtained by metallization. For this purpose, a silver paste is preferably used in order to obtain electrical contacts comprising or consisting of Ag. The paste is baked at a temperature between 680-760 ° C and is solderable.

characters

In the following the invention will be further explained with reference to figures. A conventional polycrystalline ceramic solid (reference) is compared with a polycrystalline ceramic solid (sample) according to the invention:

FIGS. 1A and 1B show scanning electron micrographs (BSE images) on a conventional (FIG. 1A) and on a solid (FIG. 1B) according to the invention.

FIGS. 2A and 2B show scanning electron micrographs (SE images) on a conventional (FIG. 2A) and on a solid (FIG. 2B) according to the invention.

Figures 3A and 3B show elemental distribution patterns for the element magnesium on a conventional (Figure 3A) and on a ceramic solid according to the invention (Figure 3B).

Figures 4A and 4B show tables with EDX results for the elemental composition of the main phase (Figure 4A) and the minor phase (Figure 4B) of a conventional ceramic

Solid state. FIG. 5 shows results for elemental composition (EDX results) of the main phase of the invention

ceramic solid.

Figures 6A and 6B show EDX / EBSD superposition images (EBSD = electron backscatter diffraction) for a conventional (Figure 6A) and solid state (Figure 6B) invention.

FIGS. 7A and 7B show the results of evaluation of grain sizes for a conventional one (FIG. 7A) and FIG

solid bodies according to the invention (FIG. 7B).

FIG. 8 shows the electrical capacitance versus the temperature for a polycrystalline ceramic solid according to the invention and a conventional polycrystalline one

ceramic solid with minor phases.

FIG. 9 shows the relationship between dissipation factor and temperature for a polycrystalline ceramic solid according to the invention and a conventional polycrystalline ceramic solid with secondary phases.

FIGS. 10A and 10B show a container with a gap (FIG. 10A) and a completely closed container (FIG. 10B) as they are used to produce the sample and to produce it

Solid bodies can be used according to the reference.

In the following the figures and results are described in detail: Figures 1A to 2B are each raster electrons

Microscopy shots. These and the other electron micrographs described below and

Measurement results were taken on a Zeis Merlin Compact VP

Scanning electron microscope obtained. All four images were magnified 1000 times at an acceleration voltage of 20 kV in a vacuum of approx.

Recorded 2.2 * 1CV ⁶ mbar. The sample, as well as the

Reference, are each polycrystalline, ceramic

Solids. Both sample and reference were sawed, embedded, ground and polished for Scanning Electron Microscopy. To avoid charges, the cut was steamed with a thin layer of carbon.

Figures 1A and 1B show backscattered electrons (BSE) images from the reference (Figure 1A) and the sample (Figure 1B). By contrast, FIGS. 2A and 2B show secondary electron contrast images (SE images, SE = secondary electrons), the reference (FIG. 2A) and the sample (FIG. 2B). The BSE and SE images of Figs. 1A and 2A were respectively recorded at the same location of the reference. Likewise, the BSE and SE images of Figures 1B and 2B were recorded at the same location on the sample. BSE images allow good material contrast (phase contrast), while SE images can provide more topographic information. The BSE images of reference and sample show dark spots. These dark spots are predominantly due to pores, because both the sample and the reference have a certain, albeit slight, porosity. The light background, on the other hand, is due to the main phase. As already mentioned, SE images allow conclusions about the surface topography of the investigated solid. Also in the SE images of Figs. 2A and 2B are the dark spots seen on the BSE images, however, the SE images allow the reference of Fig. 2A to be between two different types of dark ones

To differentiate, while in Figure 2B none

different types of dark spots can be recognized. FIG. 2A contains dark areas with a bright border and those without a bright border. The dark areas with a bright border are due to pores. The bright border is caused by the change in the topography in the area of a pore. However, FIG. 2A also has dark areas without a bright border, which are not due to pores but to secondary phases, as will be explained in more detail below. Dark phases associated with the minor phase are marked by circles in FIG. 2A and also in FIG. 1A. In contrast, only pores, but no secondary phases can be seen in Figure 2B. The reference is characterized by a considerable proportion of secondary phases, while the sample according to the invention has no secondary phases

having. The secondary phases marked in FIGS. 1A and 2A are characterized by a partially needle-shaped or edged structure. They have a different chemical

Composition as the otherwise bright main phase, which forms the background of the recordings. This is done in particular by means of an investigation of the chemical composition of the major and minor phases of the reference as well as the sole

Main phase of the sample clearly (Figures 3-5).

Figures 3A and 3B show elemental distribution patterns for the element magnesium for the reference (Figure 3A) and the sample (Figure 3B) obtained by means of SEM-EDX measurements (EDX stands for Energy Dispersive X-Ray Spectroscopy). For EDX measurements, an Oxford SDD 80 mm ² detector was used (Aztec). The pictures show the distribution of magnesium for the reference and the sample prepared according to the method of the invention. The element distribution images in turn show the same locations already shown in FIGS. 1 and 2. Bright spots show a high

Magnesium content. From the comparison of FIGS. 3A and 3B, it can be seen that the reference has Mg-rich sites. The minor phase present in the reference is thus a Mg-rich minor phase. With the help of element distribution images, the proportion of the minor phase on

quantify polycrystalline ceramic solid of the reference. The evaluation of Mg element distribution images on conventional, ceramic solids shows a high proportion of unwanted secondary phases. Thus, the reference has a secondary phase which, on average through a section through the solid, is an area fraction of the minor phase relative to a sectional area through the solid of 0.7 percent. In contrast, the inventive ceramic solid of Figure 3B is free of Mg-rich

Put. He has no side phase.

Further elemental distribution images were also recorded for elements C, 0, Ti, Nb and Pb for the reference and the sample. It is noteworthy that the lead element distribution images (Pb times recordings) for the sites that belong to the Mg-rich minor phase of the reference, reveal a depletion of lead compared to the main phase. From the various elemental distribution images, it becomes clear that the sample is free of unwanted secondary phases, while the reference has a Mg-rich and at the same time Pb-poor secondary phase. The main results of Examination of the elemental composition of the main phase of the sample and reference, as well as the minor phase of the reference are shown in the tables of FIGS. 4A, 4B and 5

summarized .

Figures 4A and 4B show the EDX results

comparative scanning electron microsphere for the reference, wherein Figure 4A shows the EDX results of the main phase and Figure 4B shows the EDX results of the minor phase of the ceramic solid. Figure 5 shows EDX results from comparative scanning electron microspheres for the sample. In each case 4 EDX spectra were recorded. The measured shares of

Elements 0, Mg, Ti, Nb and Pb are plotted in atomic percent for each spectrum. From the 4 spectra, the average values for the proportions of Mg, Ti, Nb and Pb were respectively formed. Experience has shown that the proportion of light elements, such as oxygen, is underestimated in EDX measurements. A

Normalization to determine the empirical formula was therefore expediently carried out so that the total content of Mg + Ti + Nb in the sum corresponds to 1. The coefficients thus obtained are the associated chemical formula

also to be taken from the tables. For the

The main phase was also on the basis of the

Weighing expected coefficients indicated. A comparison of Figure 4A and 5 shows that in the case of

According to the invention, the lead content deviates less from the ideal composition. The lead content of

The main phase of the reference, at 0.941, is significantly lower than the ideal 1.0. In contrast, the main phase of the sample comes closer to the ideal value. Finally, conclusions can be drawn from FIG. 4B about the chemical composition of the secondary phase. As mentioned earlier, the minor phase is rich in Mg and low in Pb. The Nb content is slightly higher than in the main phase. Without through the

Theory seems to be bound to describe the minor phase most likely by a formula Mg2 _/ 3 bi _/ 303 phase.

Figures 6A and 6B show EDX / EBSD superimposition images (EBSD) of the reference (Figure 6A) and the sample (Figure 6B). For the recordings an FSD (English Forward Scatter Detector) was used. The EBSD measurements were performed on etched samples. The following settings were selected for the reference and sample: Acceleration voltage 20.00 kV; Sample tilt (degrees) 69.99 °; Hit rate 94.25% to 94.99%; Uptake rate 66.25 to 66.35 Hz. The phases for the images were based on the phase Pb (Mgi _/ 3Nb2 _/ 3) O3: a = 4.05 Å; b = 4.05 Å; c = 4.05 Å; =

90.00 °; β = 90.00 °; g = 90.00 °; Room group 221; Database ICSD. From the pictures can be especially the

Grain sizes of the crystallites of the reference and the sample compare well with each other. The sample is characterized by significantly larger particle sizes.

A quantitative evaluation of the differences in the

Grain sizes are shown in Figs. 7A and 7B. The

Determination of the equivalent circle diameter (ECD) has already been explained above. It can be seen in particular from FIGS. That the sample according to the invention (FIG. 7B) has a significantly larger d5 _Q , measured at 5.32 μm, than

numerical median value by static image analysis, as the reference at 3.79 pm (Figure 7A). The total distribution of grain sizes is in the sample

thus shifted to larger grain sizes compared to the reference sample. This shows that the method according to the invention, by means of which the sample was produced, is not limited to the Avoidance of secondary phases, but at the same time leads to larger crystallites, resulting in improved electrical

Capacities (Figure 8) and lower power losses (Figure 9) can be achieved.

Figure 8 compares the electrical capacitances of the sample and the reference. The counts show the dependence of the

electrical capacitance, expressed in nanofarads [nF], from the temperature in degrees Celsius [° C]. The measurements were carried out at 200 kHz and 1 V, respectively. Both solids have a maximum of the electrical capacity in the range of

Temperature between 30 and 42 ° C. This is on the

comparable chemical composition of the main phase. , From the comparison of the obtained measurement curves it becomes clear that the electrical capacity of the sample is continuous over the entire measured temperature range

is significantly higher than the electric capacity of the

Reference. The capacity is on average about 5% higher for the sample according to the invention.

FIG. 9 shows the dependence of the loss factor on the temperature in degrees Celsius [° C]. The measurements were carried out at 200 kHz and 1 V, respectively. For sample and reference, the loss factor decreases with increasing temperature. In contrast to the reference, the loss factor for the

important temperature range between 20 and 45 ° C, however, significantly lower, which means that in an application of the solid according to the invention in electrodes low

Power losses are obtained. This leads to a higher efficiency and above all to a lower one

Self-heating. Figures 10A and 10B illustrate how the reference and the sample as described in Figures 1-9 can be obtained. The sample is a polycrystalline ceramic solid according to the invention according to the first aspect of the present invention, which is obtained by means of the method according to the invention of the fourth aspect of the present invention

present invention. It was the

Sintering step F) in a container according to Figure 10B with a container body (1) and a container plate (2) completed. Together they form a closed container in the interior (3) of the sintering step F) of the method according to the invention is completed. For this purpose, one or more green bodies in the interior (3) of the closed container are arranged. The closed container forms

closed system that prevents outgassing of PbO.

The shape of the container can be varied. The material of the container is chosen so that it is not suitable for the absorption of PbO and PbO is impermeable, so that a particularly effective control of the lead balance during sintering is made possible. In contrast, conventional

Polycrystalline ceramic solids needed for high-capacitance electrodes to treat patients are not sintered under adequate lead-control. This leads to the outgassing of PbO during sintering and thus to inhomogeneities in the solid state. Above all, the inventors of the present invention were able to find out that this is responsible for the formation of undesirable

Secondary phases, as found in conventional ceramic solids. The secondary phases lead to the reduction of capacity and give conventional ceramic

Solids, a yellow tint. The consequences of a

lack of lead budget control are exemplified by the

Reference shown. The reference can be made by sintering in an arrangement according to FIG 10A are obtained. Figure 10A shows a container body (1) and the container plate (2) and means for providing a gap (4) between

Container body and container plate. The container of Figure 10A thus has a gap. The size of the gap is 5 mm. Between the interior (3) of the container and the environment thus a certain gas exchange is possible. This results in a part of Pb of the solid being released during sintering in the form of PbO. The reference obtained in this way has in contrast to the sample a yellow tint.

Synthesis of the sample and reference

The sample and reference were obtained as follows:

In both cases, first green bodies were the same

Composition produced. For this purpose, in each case 34.9494 kg Mgi _/ 3Nb 2 _/ 3C> 2, 83, 8043 kg Pb 3Ü 4 and 1.7488 kg TiCk were weighed.

The starting materials were pre-ground to a target particle size d50 of about 1.0 pm in 100 liters of deionized water. The mixture thus obtained was subjected to spray drying. Thereafter, the mixture was calcined at 820 ° C for 6 hours, ground to a particle size d50 of about 0.8 pm and spray-granulated with 3 wt.% PVA binder.

From the ceramic granules, the green bodies were made by pressing. The compact density was 4.8 g / ml. The green bodies were decarburized at 450 ° C.

The sample was obtained by sintering in a closed MgO container according to FIG. 10B. The reference was obtained by sintering in a MgO container according to FIG. 10A. The gap was 5 mm. As sintering temperature were each selected 1250 ° C. The hold time at 1250 ° C was 4 hours. The volume filling level in the case of the sample was approx.

45 vol. %. The invention is not limited by the description with reference to the embodiments. Rather, the includes

Invention every new feature as well as every combination of

Features, which includes in particular any combination of features in the claims, even if this feature or this combination itself is not explicitly in the

Claims or embodiments is given.

Claims

claims

1. Polycrystalline, ceramic solid

including

a main phase having a composition of the following general formula:

(1-y) Pb _{a (} Mg _bN b _c) 0 _3-e + yPb _a Ti _d 0 ₃

With

0, 055 <y <0.065

0.95 <a <1.02;

0.29 <b <0.36;

0, 63 <c <0.69;

0.9 <d <1.1;

0 <e <0, 1;

and optionally one or more minor phases, wherein at each section through the solid state of the

Area fraction of the secondary phases in relation to an arbitrary sectional area through the solid is less than or equal to 0.5 percent or wherein the solid body is free from

Secondary phases is.

2. Solid according to the previous claim, wherein at

each section through the solid, the area ratio of the minor phases based on any section surface through the solid is less than or equal to 0.3 percent, preferably less than or equal to 0.05 percent.

3. Solid according to one of the preceding claims, wherein the main phase is formed from grains whose average grain size d5 _Q , measured as a numerical median value by static image analysis, between 4 and 9 pm

is.

4. An electrode comprising a solid according to any one of claims 1 to 3 and further comprising an applied on the solid electrical contact.

5. Method for producing a polycrystalline,

having ceramic solid body

a main phase having a composition of the following general formula:

(1-y) Pb _{a (} Mg _bN b _c) 0 _3-e + yPb _a Ti _d 0 ₃

With

0, 055 <y <0.065

0.95 <a <1.02;

0.29 <b <0.36;

0, 63 <c <0.69;

0.9 <d <1.1;

0 <e <0, 1;

Area fraction of the minor phases is less than or equal to 0, 5 percent in relation to any sectional area through the solid

or wherein the solid is free of secondary phases, comprising the method steps:

A) providing starting materials comprising the

Elements Mg, Nb, Ti and Pb;

B) producing a mixture comprising the

starting materials

C) calcining the mixture to produce a

calcined mixture

E) processing the calcined mixture into a

green body

F) sintering of the green body,

being to control the lead budget Step F) takes place in a closed system, and / or

in step A) or other steps preceded by step F), a starting material containing Pb is added in excess.

6. The method according to the preceding claim, wherein in

Step A) provides a first starting material which is Mgi _/ 3Nb2 _/ 3C> 2.

A process according to any one of claims 5 or 6, wherein in step A) a second starting material is provided which is T1O2.

8. The method according to any one of claims 5 to 7, wherein in step A) a third starting material is provided, which is PbO or Pb3Ü4.

9. The method according to any one of claims 5 to 8, wherein the mixing of the starting materials in step B) is carried out by wet grinding.

A process according to any one of claims 5 to 9, wherein the calcination is carried out in step C) at a temperature between 800 and 860 ° C.

11. The method according to any one of claims 5 to 10, comprising a step D), in which T1O2 and / or Nb2Ü5 is added to the calcined mixture, wherein the proportion of added T1O2 and / or Nb2Ü5 based on the

Weight of the calcined mixture is preferably 0.01 to 0.4 weight percent.

12. The method according to any one of claims 5 to 11, wherein step E) comprises:

Grinding the calcined mixture,

Putting the calcined mixture with a binder,

Spray-drying the calcined mixture with binder to produce a ceramic granulate

- Pressing the ceramic granules to produce the green body.

13. The method according to any one of claims 5 to 12, wherein

Step F) is carried out at a temperature of 1150 to 1280 ° C.

14. The method according to any one of claims 5 to 13, wherein step F) takes place in a closed system, which is a closed container (1,2), wherein the container is preferably at least one of the materials selected from the group of AI2O3 , ZrCb and MgO or consists thereof.

15. The method according to claim 14, wherein the closed container (1,2) has an interior space (3), in which one or more green bodies are arranged, so that the Volumenfüllgrad all green bodies with respect to the volume of the interior (3) at least 30 vol. %, preferably at least 40 vol.% Is.

16. A method for producing an electrode according to

Claim 4 comprising a method for producing a polycrystalline ceramic solid according to any one of claims 5-15 and a thereto subsequent step to provide the solid with an electrical contact.

17. The method according to the preceding claim, wherein the

electrical contacting by applying and

Burning a paste is carried out, wherein the baking is preferably carried out at a temperature of 680 to 760 ° C.